This invention relates to a sorbent moulded or shaped body comprising micro-porous or meso-porous adsorbents, and a method for production and use thereof. The moulded bodies serve to store process heat and cold, whereby a vaporous working medium is expelled from the moulded body by the introduction of heat energy and the working medium is optionally condensed. The working medium that is optionally previously vaporised is adsorbed in gaseous form.
As a coated, packed or bundled form, moulded bodies provide sorptive thermal energy storage preferably with the help of water vapour working medium as for instance in the fields of heating, cooling/air conditioning, above all for making use of natural thermal sources such as terrestrial or solar heat. With the aim of energy storage, there exist applications everywhere where thermal energy must be available for temporary use periods, which should not coincide with periods of heat generation or with their accessibility. The economical scope of the application of moulded bodies, comprised of micro-porous or meso-porous sorbents, is to obtain higher space-time yields of the apparatus by which the energy transformation, for instance that of heat storage, can be achieved. In this case, the external shape and the geometrical dimensions of the sorbent shaped bodies can be suitably adjusted to the corresponding heat exchanger, such as to the geometry of the internal wall of the heat reservoir.
State of the art in the field of silicate heat storage media is characterised by micro-porous and meso-porous sorbents from which the water of crystallization can be removed through heat input without damaging their framework.
Zeolites
The production of zeolites is described in published information regarding “Baylith®—Informationen”, among them “80.100—general product description”, “81.503—Technical Properties” and “81.505—Technical application features”, Bayer-Werke Leverkusen, as well as on “Zeosorb Molecular Sieves”, Bayer AG Bitterfeld-Wolfen.
For the achievement of higher mass and heat space-time yields specially for those processes which can be influenced by catalytic action, alumosilicate like zeolites are mainly employed. They occupy anion frameworks that are preferentially subjected to chemical modification processes (DE 44 33 120 A 1). Usual silicalite sorbents production techniques consist of impregnating a matrix with activating components such as through infiltration process to achieve cation exchange. High heat storage capacity can be acquired through employing magnesium containing zeolite granular materials (DE 33 12 875 A1). Hydrophilic materials such as salt hydrates that are subjected to a reversible hydration will be deposited on usually temperature stable sorbing matrix. Examples are given in DE 43 05 264 A1, in which calcium chloride is placed in a zeolite granulate (DE 43 05 264 A1) or in a silica gel (DE 197 34 887 A1). The chemical composition of a zeolites type NaX is for example Na12(AlO2)12(SiO2)12. zH2O, which is mostly consisted of SiO4 and AlO4 tetrahedron. The pore diameter, preferably adjusted with the size of water molecule, lies within 3-10 Å depending on the type of the molecular sieve. Their thermal stability can reach up to a temperature of 850° C. and their hydrothermal stability is up to about 400° C.
In cyclically accomplished processes, such as the charging of heat storage through desorption of the water vapour working medium and its discharging through adsorption on zeolites, not infrequently cycle numbers from 4,000 to 10,000 are attained. However, the almost entirely adsorbed water is only released by zeolites through application of process temperatures of 200° C. to 450° C. Thus, the sorption capacities of zeolites are only partially utilized when solar produced low-temperature thermal heat is used. Zeolites-like metallosilicates exhibit a similar thermal behaviour but it is less efficient.
Metallophosphate: The replacement of silicon by phosphorus ions leads to zeolite-like molecular sieves such as alumina-phosphates (ALPO). A replacement of aluminium by silicon results in silico-alumo-phosphate (SAPO). The chemical composition of ALPO corresponds to a large extent to xR.Al2O3.1.0±0.2 P2O5.yH2O
The composition of water-free SAPO is about 0-0.3R(SixAlyPz)O2, wherein R is anine or ammonium salt. The AlO4-tetrahedrons are seated together with PO4-tetrahedrons. In the metallo-alumino-phosphates (MeALPO) of 0-0.3R(MexAlyPz)O2 composition, silicon is additionally replaced by numerous other elements. Common feature to all metallophosphates is the formation of new structures with outstanding characteristics for water storage. Storage materials whose pore diameter favourably accounts to 2 to 13 Å are mainly selected. Thermal stability even at temperatures up to 1000° C. is exhibited. Their hydrothermal stability for temperatures up to 600° C. is appreciably high. During the sorption smooth hysteresis curves appear. To the state of knowledge through sample tests it is confirmed that with repeated adsorption and desorption up to 60.000 cycles, practically no changes in the isotherm forms of water can be recognized. It is of special advantage that the sorption isotherms of water exhibit an s-form process with an abrupt rise within a very low pressure interval. Within this range through pressure drop to few mbar, an extensive desorption is achieved under normal temperature. In comparison to silica gel, a 4 to 6 times water amount is stored. Metallophosphates are particularly preferred for storage of solar heat due to their low temperature favoured desorption in the device. It is intended to build significantly smaller storage systems and also sorption heat pumps on the basis of the new sorbents due to the high temperature change.
Granules/Moulded Bodies:
Synthetic sorbents that are modified to intended purposes are usually available in a finely grained crystal form. Mostly their crystal size does not exceed a maximum of 500 μm. However, for an effective heat storage application in the apparatus, the bulk of these crystals allow only limited flow-speeds of the vaporous materials due to their limited gap volumes and higher flow resistance. Pelleted granules that are made into porous moulded bodies with binder which bodies are random clusters of the pelleted granules are favourably applicable. These moulded bodies exhibit larger transport pores and cavities as well as flow channels, whereby higher speeds for the flow of the working medium are permitted and upstream distances are significantly shortened for the water vapour working medium mass transfer. The total process-time is limited by the material and heat exchange processes and is determined by the pore size of the sorbents themselves. An advantage of application of moulded bodies is that they are packable between heat directing devices and in the exchangeability of individual components particularly for the purpose of designing and dimension enlargement in module-like arranged heat storage. It seems also possible to limit the requirement of installed heat directing components in the heat storage through enlargement of the moulded bodies. So far there are only the so-called “zeolite moulded bodies” as a standalone category within the outlined state of the art.
Thermal Conductivity
In random bulk sorbents with a high storage capacity, heat energy with low-loss is introduced and transferred into the interior space flowing heat carrier medium, whereby if possible heat energy is not released irreversibly to the environment (e.g. DE 34 18 005 A1, DE 36 43 668 A1, DE 44 37 950 A1, EP 0,091,095 A). To obtain high energy density, an optimal ratio between heat transfer surface area and the storage volume is selected. The heat source in the longitudinal and transverse directions is arranged in such a way that the created material and temperature gradient are instantly balanced. However, it is unfavourable that a pronounced and not ultimate transition features in the dynamics of heat storage is observed during cyclic load exchange. Particularly during a scale enlargement in a geometrically intended main expansions, unwanted intermediate states arise in which the temperature change does not mainly take place in a gradual way due to disabled heat transfer and it is temporally and spatially blurred.
The disadvantages that arise in the case of mineral sorbents as a result of bad thermal conduction are already overcome through metallic ductile fill materials with larger dimensions. The fill materials usually consist of a principal framework (DE 100 21 260 A1) at which the boundary surfaces are found that are flow transparent and at the same time they are mutually connected at their edges. The surfaces are good heat conducting, whereby the partially opened bodies do not fall spatially into one another. The ductility of the fill materials and also its casing (DE 100 21 260 A1) ensures a dense packing of individual elements in the reaction zone and the development of the majority of heat-transferring contact surface areas in the space expansions of the heat storage.
Binder
The drawback of all these sorbents is that, they can be hardly integrated into a moulded body.
The binding agent that is at the beginning flow-resistance remains an important space-fill component of the moulded body, which decreases the efficiency of the sorbents by blocking the micro-pores and meso-pores.
Usually the use of already granulated or pelletted crystals with a binder leads to these disadvantages. In fact due to the larger geometrical dimensions of granules, larger gap volumes arise that are favourable for the flow channel because of lower pressure losses. But regarding lower packing density, it affects the economic efficiency of the device altogether unprofitably.
Also flow-resistance and hardenable binder were already enriched only in the permeable surface of sorbing moulded bodies in order to improve their surface and structural stability altogether. This can be achieved by means of force field processes such as through sedimentation or filtration (DE 103 01 099 A1). Molding preforms are used that are impregnated with the spatially unevenly distributed bulk of the binder and are thermally pre-hardened at low temperatures.
Material and energy exchange: There are already known sorbing moulded bodies, which are provided with fluid permeable casings made from ceramic or metallic materials for the purpose of the good mass or energy exchange through the walls that bounded them (EP 0 1 403 80 A).
During the heat storage by means of highly effective ALPO or SAPO that have higher hydrothermal stability a special binder is required, which hardens at low temperatures without considerably decreasing their sorption ability and they present in likely low proportion in the moulded body.
Regeneration
Although the adsorption of vaporous working medium on silica based storage material can take place desirably under normal temperature, an achievable complete desorption and a targeted high degree of restoration of cyclic working capacity must be intended at higher temperatures usually of approximately 500° C. for the active components of the sorbing moulded bodies. The considerable charging and thus the temperature changes affect permanently the durable integration of powders or granulates into the porous moulded bodies. Since internal defects arise through tensions which are caused by heat changes, the moulded bodies must exhibit a high stability. These must be trapped by the stabilized walls for the sake of longer durability of the moulded bodies. Thus, the enhancement of the heat and/or cold storage is intended through the increment of the sorption capacity and the rise of the energy density also under improved mechanical characteristics of the moulded bodies.
The bad thermal conduction remains still unfavourable in particular for larger moulded bodies, since they are predominantly made up of mineral components as an insulant-like materials.
Task Setting
Therefore, the basic task of the invention is to eliminate the mentioned mechanical structure like heat and flow technical disadvantages of the described solutions of sorbing moulded bodies, whereby for sorbents with improved efficiency an improved heat guidance is also to be considered.
Constitution of the Moulded Bodies:
The task is solved by a moulded body, which possesses a metallic grid network-like cage structure and an internal likewise net-like heat conducting surface. The conducting surface according to the invention is a means for the better passage of heat flows and for the increment of stability as well as the shape of the moulded body.
From geometrical point of view, the conducting surface is formed from laterally expanded and between edges stretched produced guidelines of at least second order, which are bounded at the two transverse ends by second order curves. These edges represent circle, ellipse or parabola segments. The two bounds of the cage structure are connected, in each case in at least three upper points with a limiting edge as well as in three lower points with the second limiting edge of the conducting surface. In the longitudinal direction and thus the main expansion of the moulded body, the conducting surface exhibits the form of a spatially curved diagonal surface. The diagonal surface consists of two homogeneous parts, which are symmetrically reflected around the middle transverse axis in one of the transverse extensions.
From the physical point of view, the conducting surface represents a minimum surface in a cylindrical or rectangular body form for thermal conduction. Within the moulded body the conducting surface supports itself at the points of contact in an elastic way at the cage structure and it is optionally connected with the bounds of this structure.
With low expenses of material supply, an optimally high heat transfer character is adjusted within the moulded bodies and it is further send to their externally bounded cage structure. Altogether a sideway stable and proper heat conducting lattice structure develops within and outside of the moulded bodies.
The cage structure can consist of a woven fabrics, plaits or braids, knitted fabrics, or fibrous web or clutch that are preferably lattice-like or net-like and are metallic. In addition, the structure is at least single layer and can be implemented roughly by windings into multiple layers.
The heat carrier pipes can be thereby conventional pipes; they can also be a specially made pipes that make possible a better flow and heat transfer within the heat storage. In this way the pipes can be a so-called indented pipes, by which in their inside a highly turbulent flow is created with the working medium so as to make an improved heat transfer over the walls of the tube be possible. A similar effect is obtained by a sintered pipes, which exhibit roughness in their inside wall. Also the moulded bodies can be modified into disc-like objects, that connect flow technically related pipes with one another analogous to heating systems. In this way roughly parallel arranged or meandered pipes can be connected with one another over the damper for the inlet and outlet of the heat carrier medium.
Highly active sorbent is found within the cage structure with the conducting surface in form of agglomerate crystals or palletised granules, which are fused with one another through the binder in form of a random bed.
The geometrical boundary of the moulded bodies can be barrel-shaped, cylindrical, prismatic or polyhedral. The cage structure with the conducting surface and with the internal available powders or granules is partially deformable at least during its production process. These fulfill preferably the structural conditions of a rectangular or triangular pitch configuration of the internal heat directing devices on the bottom reflectors of the heat storage. They get closer in their form to the peripheries of the heat carrier pipes like in any case at individual points of contacts.
The flow of the working medium takes place in cavities preferably in the form of a compartment or wedged shaped inter-particle spaces or also over the tolerance gap that is developed between the moulded bodies and the heat carrier pipes. The material exchange of the moulded bodies takes place mainly over its front side and lateral surface. The heat exchange takes place over the cage structure connected with the conducting surface and with the neighbouring heat carrier pipes. Due to the high affinity of the sorbents to the vaporous working medium and consequently to high impulse forces of the sorption process, sufficient free cross sections are adjusted in all cavities for the flow of the working medium.
The external geometrical dimensions of the moulded bodies exceed significantly the size of the granules. Accordingly, high bulk density and higher space utilisation rate are adjusted for the sorbents in heat storage. The mesh sizes of the cage structure are however smaller than the main dimensions of the granulated sorbent bodies. For the purpose of the passage of the vapour of the working medium, during the application of powders in the moulded bodies, the mesh size of the cage is defined merely on a minimum required quantity. The mesh size of the conducting surface exceeds the size of the powders and can also exceed the size of the granules and it shall allow unrestricted flow of the moulded bodies in the preferred direction.
It is appropriate to combine the interior of the sorbent with special flow channels. These facilitate the admission of the working medium into the spaces of the moulded bodies, which lies suitably towards its main dimension but yet outside the sorption front. Altogether such a proportional cross flow of the working medium is achieved, which get into the heat storage over both the front surfaces and also over the lateral surfaces of the moulded bodies.
Methods for Production:
The lattice cage of the moulded bodies is pre-fabricated through rolling a smooth preferentially metallic network or from another wired and sharp mold-carrier. The network of the mold-carrier can also be a woven fabrics, plaits or braid, knitted fabric, or fibrous web. It is a netlike stocking material that is suitably cut into lengths. The conducting surface that is brought into the mold-carrier is plugged, stapled, sewed or simply attached to the bounds of the cage. The applied and those particles inserted into the moulded bodies are aluminosilicate powders or pre-moulded sorbing granules. They exist in a sphere, cylinder, barrel or other forms deviating from these prism geometry that preferentially refers to ALPO, SAPO and MeAPO.
The pre-fabrication of the moulded bodies takes place by pre-mixing the mineral powder and/or the pre-moulded granules with low viscous fluidic binders or from its moderately viscous or pasty components and the mixture is filled into the cage with the conducting surface. The fluidic viscous binder penetrates initially the entire gap volume. The binder should be enriched preferentially at the peripheral zone of the moulded bodies in order to ensure the entrance of the working medium through micro-pores and meso-pores with only low inhibitions for diffusion. Thus, the portion of the binder in the interior remains low and reduced on a required degree. As a function of the dimensions of the sorbening particles, the fill can take place through pressing with the help of a plunger or a piston movement of one or suitably from both transversally expanded boundary surfaces of the moulded bodies.
Familiar binders are preferably used, which are at low temperatures pre-dryable and hardenable. These are usually pre-polymer of alkaline silicates such as water-glass or silicon-organic viscous pasting agent like silicone. Phenol formaldehyde resins, polyvinyl resins and polyacrylates, with only slightly intended low internal binding firmness for the sorbents, can serve as additional binders. Also polyurethane and lattices increase the firmness within the moulded bodies only moderately. Cellulose derivatives as matrix creators for powders and granules are only temporarily available, during the pre-solidification process in the moulded bodies remained binders, and they can be partly removed by extraction again. Thereby, the undesired blocking of the micro-pores and meso-pores in the sorbents by the binder remains to a large extent reduced.
A chemical treatment of the binder can be caused by the introduction of additional adhesive and solidifying, however fluidic chemically reacting materials, into the components of the moulded bodies during the partial elimination of the binder. This can be occurred by means of acids or bases for water-glass containing binder, which accelerate the polymerisation and condensation of the available silicate functional groups. With other silicates and hardenable binders this can be caused by adding reactive fluidic components for the development of the pre-polymers.
In the wall-bounds the binder is locally restricted and is applied preferentially in higher proportions, where it is essential for the maintenance of the structure stability of the moulded bodies and thus for its structure-forming effect. Due to higher temperature resistance, in these bounds common inorganic binders are used preferentially like aluminium hydroxide hydrates, clays and silica gel. Likewise embedding can take place in a matrices made of silicic acid or aluminiumoxid hydrate as well as in bentonite and special clays like metakaolinite. Also a carbonation of the particles embedder and originally water-soluble pitch acid is possible.
Fluidic binders are brought into the wall-bounds by means of infiltration, whereas pasty ones if necessary through overpressure and under creation of a pressure cushion within a press rooms to one or both of the transversal bounding surfaces. The binder is enriched thereby in a relatively thin layer and penetrates into the regions with higher boundary surface forces and thus adhesive force, particularly during application of granules. It adheres preferentially to the points of contact of the crystals and granules and fills only partially the interiors of the moulded bodies and the vacant spaces that are necessary for the mass transfer between solid components. Moderately pasty binders are already applied during the pre-fabrication on the lattice structure of the moulded bodies and under pressure they are pressed into the exterior surfaces.
A stepwise or sudden distribution that is forwarded into the interior is adjusted by means of binders of the moulded bodies present between the granules prior to or during the structural solidification. This can be caused when in the core zones of the moulded bodies lower proportion of the first binder exists. However in the auxiliary lying peripheral zone, higher portions of a second binder can be accessible.
The moulded body is pre-solidified under heating through compression of the lattice cage together with the sorbents. Thereby those which are stated under heat input, at least two layer die stocks, heat up also the lattice cage of the moulded bodies, whereby over the conducting surface at the same time a distinctive good heat entrance is made into its inside under intensive heat balance for the purpose of binder drying process. It is also possible to put and compress the lattice structure in addition together with the binder on the moulded bodies. It follows a post-drying with increased temperatures and/or also activation of the moulded bodies. This can take place in a suitable gas atmosphere. All moulding processes associated with heat balance take place due to improved thermal conduction even with larger dimensions of the moulded bodies within reduced periods of times compared with those conventionally manufactured moulded bodies without conducting surface.
A stable and highly mechanically resistant coating region develops in the wall-bounds of the sorbing moulded bodies, which is arranged toward the original pressing effect. However, in the central and axial neighbouring regions the binder portion is reduced.
In the modification of the moulded bodies fine fibrous and/or fine dispersed metal components with dimension in millimeter region are also additionally available in its interior for the purpose of improved thermal conduction. This is above the size of the silicalite crystal, however below the basic dimension of the granules and proportionally in contact with the conducting surface of the moulded bodies. Where appropriate deformed stripe-, fibre- or film-like components of metals or other heat-conductive materials, whose basic dimensions lie above those of the granules, can also be introduced. Further components of the moulded bodies are the portion of the wetting agents and adhesion mediator for the components of the moulded bodies between the sorbing particles.
Since the pre-solidification of the binder takes place under simultaneous pre-heating of the pre-form and the corresponding pre-heating temperatures for water-glass containing binders lies below 200° C. preferentially 150° C., there is no damage to expect in particular for alumino-phosphates, silico-alumo-phosphates or metallo-alumo-silicates. Temperatures between 400° C. and 600° C. in an inert gas conditions is favourably used to bake and activate that similarly does not lead to structural changes.
Particularly favourable effects are obtained by the fact that the active components of the sorbing moulded bodies in contrast to the state of the art do not or insignificantly change their lattice structure at higher temperatures during the charging and discharging heat storage processes, so that a long durability of the moulded bodies and an improved effectiveness at the same time enhanced life time is attained.
The characteristic features of the invention are derived from the elements of the claims and the stated descriptions. Both the single and a combination of several of these features represent a favourable method for which a protection is applied through this publication.
The nature of the invention consists of a combination of known (moulded bodies made of powders and/or granules, binding agents, etc.) and new elements (the production of the moulded bodies by means of a cage and conducting surface), which influence mutually and show new entire positive effect on their application and the strived success to achieve higher space-time yields while storing process heat and cold than the state of the art.
The advantages of the inventive sorbent moulded body is thus an optimal as well as possible co-actions of heat directing and the reaction technical efficiency of alumino-phosphates, silico-alumo-phosphates or metallo-alumo-silicates as well as in their flow-technical action during the material and heat exchange so as to achieve high space-time yields while storing process heat and cold.
The method is not limited only on the production of sorbent moulded bodies. Other moulded bodies, for instance those containing non-adsorbing granules can be produced in the same or similar manner through infiltration within a lattice structure. In this way a sinter-like fused moulded bodies are developed from the coarse dispersed granules that are characterized favourably by lower proportion of binder and higher gap volumes, whereby the walls are strengthened by higher proportion of the solidifying binding agents.